This invention relates to a polyoxymethylene composition having excellent antistatic properties.
Acetal resins such as polyoxymethylene are widely used in automobile parts, in parts for electrical appliances and sound equipment, and the like due to their excellent physical and chemical strengths, creep resistance, low abrasion and friction, good electrical properties and the like. But when they are used in sliding type parts, various problems in practical use often arise due to the generation of static electricity caused by friction. For example, polyoxymethylene is used in tension arms and wheels of a tape recorder, but the generation of static electricity caused by sliding results in adhesion of dust and generation of electrical noise, which remarkably reduces commercial value of the tape recorder.
It is well known in the art that the addition of carbon fibers to polyoxymethylene provides a composition having excellent abrasion and friction properties and antistatic properties. Such a composition can be available commercially but it is not used widely since carbon fibers are very expensive and the composition can be used in very limited special fields. Therefore, polyoxymethylene having excellent abrasion and friction properties and antistatic properties with low cost has long been desired.
The inventors of this invention tried to add electrically conductive carbon black to polyoxymethylene in order to give antistatic properties to polyoxymethylene, but the thermal stability of the polymer remarkably reduced when a sufficient amount of the carbon black for giving the desired antistatic properties was added to the polymer. In some cases, the preparation of a polyoxymethylene composition was impossible. The present inventors have found that when low-density polyethylene was added to polyoxymethylene together with electrically conductive carbon black, reduction of thermal stability of the resulting mixture was prevented and that there was obtained a polyoxymethylene composition having remarkably low surface electrical resistance and surface charge voltage half life, excellent abrasion and friction properties, and the like, and accomplished this invention.